This invention relates to electric lamps and particularly to a lamp assembly capable of throwing beams of light in either one or two different directions as required. Such a dual purpose lamp assembly lends itself to use as, typically, an integral combination of a fog lamp and a cornering lamp on a motor vehicle. More particularly, the invention concerns improvements in such dual purpose lamp assemblies of the type described and claimed in the above cross referenced application, which in turn is an improvement of Miyazawa et al. U.S. Pat. No. 4,663,696.
The dual purpose lamp assembly according to the noted U.S. patent comprises a relatively large fixed reflector, a movable reflector of smaller size positioned forwardly of the fixed reflector for pivotal motion about a vertical axis, and a light bulb having a filament disposed at the common focus of the fixed and movable reflectors. The movable reflector pivots between a first position, where it coacts with the fixed reflector for reflecting the light rays from the bulb forwardly of the lamp assembly, and a second position where the movable reflector reflects part of the light rays from the bulb toward either side of the lamp assembly. Thus the lamp assembly functions as fog lamp when the movable reflector is in the first position, providing road illumination forwardly of the motor vehicle. Upon displacement of the movable reflector to the second position, on the other hand, the lamp assembly serves the additional purpose of cornering lamp to supplement the vehicle headlamp system by providing additional illumination in the direction of a vehicle turn.
This prior art dual purpose lamp assembly has proved to have weaknesses arising from its mechanical construction. Being positioned upstandingly in front of the fixed and movable reflectors, the elongate stem, in particular, of the light bulb inevitably intercepts part of the light rays that have been reflected from the movable reflector. Accordingly, the complete light energy emitted by the bulb has not been utilized for the intended purposes.
In order to solve this problem, the above cross referenced application suggests that the light bulb be coaxially mounted to the fixed reflector via a bulb holder so as to extend forwardly therefrom through an aperture in the movable reflector. So arranged, the light bulb with its stem presents no substantial obstacle to the reflected rays. This solution has proved to have its own drawback, however. Although the vertical dimension of the aperture can be only slightly more than the bulb holder which extends therethrough, its horizontal dimension must be much longer to permit the angular displacement, about the vertical axis, of the movable reflector between the two working positions without interference with the bulb holder. Such a large aperture reduces the reflective surface area of the movable reflector and so makes it impossible to provide illumination of desired intensity distribution.